KR20140030465A - Steel plate and method for manufacturing of the same - Google Patents
Steel plate and method for manufacturing of the same Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/28—Normalising
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
Abstract
Description
본 발명은 강재 제조 기술에 관한 것으로, 보다 상세하게는 장시간의 PWHT(Post-Weld Heat Treatment) 이후에도 저온인성이 우수한 강재 및 그 제조 방법에 관한 것이다.
TECHNICAL FIELD The present invention relates to a steel material manufacturing technique, and more particularly, to a steel material excellent in low-temperature toughness even after long-time PWHT (Post-Weld Heat Treatment) and a manufacturing method thereof.
화력발전 설비 등에 적용되는 압력용기용 강재는 주로 후물이 사용된다.Steels for pressure vessels to be applied to thermal power generation facilities are mainly used for precious metals.
최근 압력용기의 대형화 추세에 발맞추어 고강도, 고인성 및 극후물화 양상이 뚜렷하게 나타나고 있다. 이에 따라, 압력용기용 강재에 있어서, 고강도 및 고인성의 성질을 가지는 QT(Quenching & Tempering) 강재의 제조와 더불어 강재의 두께를 상향시키는 연구가 활발히 진행 중에 있다.In recent years, high strength, high toughness and extreme post-mortification tendency have been evident in line with the trend toward larger size of pressure vessels. Accordingly, in the steel material for pressure vessels, studies have been actively made to increase the thickness of the steel material in addition to the production of QT (quenching & tempering) steels having properties of high strength and high toughness.
그러나, 두께 80mm 이상의 극후물재는 강재의 두께로 인해 강재의 폭 방향 및 두께 방향의 재질 편차가 크고, 중심부의 저온인성이 좋지 못한 관계로, 수요자가 요구하는 특성을 만족시키기 매우 어려운 실정이다.
However, it is very difficult to satisfy the characteristics demanded by the customers because the thickness of the steel material is large and the material variation in the width direction and the thickness direction is large due to the thickness of the steel material and the low temperature toughness at the center portion is poor.
본 발명에 관련된 배경기술로는 대한민국 등록특허공보 제10-0782761호(2007.12.05. 공고)에 개시되어 있는 두께 중심부의 강도와 인성이 우수한 극후물 강판의 제조 방법이 있다.Background art related to the present invention is a method for producing an ultra-thick steel sheet having excellent strength and toughness at the center of the thickness disclosed in Korean Patent Publication No. 10-0782761 (2007.12.05.).
본 발명의 하나의 목적은 장시간의 PWHT(Post-Weld Heat Treatment) 이후에도 저온인성이 우수한 강재를 제공하는 것이다.It is an object of the present invention to provide a steel material excellent in low-temperature toughness even after a long-time PWHT (Post-Weld Heat Treatment).
본 발명의 다른 목적은 합금 성분 및 공정 제어를 통하여 PWHT 이후에도 저온인성이 우수한 강재의 제조 방법을 제공하는 것이다.Another object of the present invention is to provide a method of manufacturing a steel material excellent in low-temperature toughness after PWHT through alloying components and process control.
상기 목적을 달성하기 위한 본 발명의 실시예에 따른 강재 제조 방법은 중량%로, 탄소(C) : 0.15~0.20%, 실리콘(Si) : 0.3~0.4%, 망간(Mn) : 1.0~1.2%, 구리(Cu) : 0.1~0.2%, 니오븀(Nb) : 0.01~0.02%, 니켈(Ni) : 0.15~0.25%, 크롬(Cr) : 0.15~0.25%, 인(P) : 0.02% 이하, 황(S) : 0.005% 이하, 바나듐(V) : 0.02~0.03%, 칼슘(Ca) : 0.001~0.003% 및 나머지 철(Fe)과 불가피한 불순물로 이루어지는 강 슬라브를 1000~1100℃에서 재가열하는 단계; 상기 재가열된 강재를 Ar3 이상의 온도에서 열간압연하는 단계; 상기 열간압연된 강재를 냉각하는 단계; 및 상기 냉각된 강재를 890~920℃에서 노말라이징(normalizing) 열처리하는 단계;를 포함하는 것을 특징으로 한다.Steel manufacturing method according to an embodiment of the present invention for achieving the above object by weight, carbon (C): 0.15 ~ 0.20%, silicon (Si): 0.3 ~ 0.4%, manganese (Mn): 1.0 ~ 1.2% , Copper (Cu): 0.1 to 0.2%, niobium (Nb): 0.01 to 0.02%, nickel (Ni): 0.15 to 0.25%, chromium (Cr): 0.15 to 0.25%, phosphorus (P): 0.02% or less, Reheating the steel slab consisting of sulfur (S): 0.005% or less, vanadium (V): 0.02 ~ 0.03%, calcium (Ca): 0.001 ~ 0.003% and the remaining iron (Fe) and unavoidable impurities at 1000-1100 ° C ; Hot-rolling the reheated steel at a temperature equal to or greater than Ar3; Cooling the hot rolled steel material; And subjecting the cooled steel material to a normalizing heat treatment at 890 to 920 占 폚.
여기서, 상기 노말라이징 열처리는 하기 식 1에 의해 정해지는 시간 동안 실시될 수 있다.Here, the normalizing heat treatment may be performed for a time determined by the following Equation 1.
[식 1] [Formula 1]
t = A × T + 10t = A x T + 10
(여기서, t : 열처리 시간(min), T : 강재 두께(mm), 40<T≤60인 경우 A=1.5, 60<T≤80인 경우 A=1.6, 80<T인 경우, A=1.7로 정의함)A = 1.5 when 60 <T≤80, A = 1.6 when 80 <T≤80, A = 1.7 when 80 <T, )
상기 냉각은 공냉 방식으로 실시될 수 있다.
The cooling can be carried out in an air cooling manner.
상기 목적을 달성하기 위한 본 발명의 실시예에 따른 강재는 중량%로, 탄소(C) : 0.15~0.20%, 실리콘(Si) : 0.3~0.4%, 망간(Mn) : 1.0~1.2%, 구리(Cu) : 0.1~0.2%, 니오븀(Nb) : 0.01~0.02%, 니켈(Ni) : 0.15~0.25%, 크롬(Cr) : 0.15~0.25%, 인(P) : 0.02% 이하, 황(S) : 0.005% 이하, 바나듐(V) : 0.02~0.03%, 칼슘(Ca) : 0.001~0.003% 및 나머지 철(Fe)과 불가피한 불순물로 이루어지며, 12시간 PWHT(Post-Weld Heat Treatment) 이후, -50℃에서 두께방향 중심부 평균 충격흡수에너지 30J 이상을 나타내는 것을 특징으로 한다.Steel material according to an embodiment of the present invention for achieving the above object by weight, carbon (C): 0.15-0.20%, silicon (Si): 0.3-0.4%, manganese (Mn): 1.0-1.2%, copper (Cu): 0.1 to 0.2%, niobium (Nb): 0.01 to 0.02%, nickel (Ni): 0.15 to 0.25%, chromium (Cr): 0.15 to 0.25%, phosphorus (P): 0.02% or less, sulfur ( S): 0.005% or less, Vanadium (V): 0.02 ~ 0.03%, Calcium (Ca): 0.001 ~ 0.003% and remaining iron (Fe) and inevitable impurities, after 12 hours PWHT (Post-Weld Heat Treatment) , The average shock absorption energy of the center in the thickness direction at -50 ℃ 30J or more.
본 발명에 따른 강재 제조 방법에 의하면, 합금 성분 및 공정 제어를 통해 결정립의 조직을 미세하게 제어하여 폭 방향 및 두께 방향의 재질 편차를 최소화하고, 장시간의 PWHT 이후에도 -50℃의 저온에서 인성이 우수한 강재를 제작할 수 있다.According to the method for manufacturing a steel material according to the present invention, it is possible to finely control the texture of crystal grains through alloy components and process control to minimize material variations in the width direction and the thickness direction, and even after PWHT for a long time, Steel can be produced.
본 발명에 따라 제조된 강재는 두께 80mm 이상인 극후물 강판에서도 -50℃에서 중심부 평균 충격흡수에너지 30J 이상의 값을 가질 수 있어 저온인성이 우수하여 용접구조용 압력용기나 초대형 컨테이너선의 외판용 소재로 활용될 수 있다.The steel material produced in accordance with the present invention can have a core average impact absorption energy of 30 J or more even at a temperature of -50 ° C even at a thickness of 80 mm or more and can be utilized as a pressure vessel for welded structures or as a material for a shell plate of a super large container ship .
도 1은 본 발명의 실시예에 따른 강재 제조 방법을 개략적으로 나타낸 순서도이다.
도 2는 본 발명의 실시예 1에 따라 제조된 강재의 광학현미경(Optical Microscope: OM) 사진이다.
1 is a flow chart schematically showing a steel manufacturing method according to an embodiment of the present invention.
2 is an optical microscope (OM) photograph of a steel material produced according to Example 1 of the present invention.
본 발명의 특징과 이를 달성하기 위한 방법은 첨부되는 도면과, 후술되어 있는 실시예를 참조하면 명확해진다. 그러나 본 발명은 이하에 개시되는 실시예에 한정되는 것은 아니며, 서로 다른 다양한 형태로 구현될 수 있다. 본 실시예는 본 발명의 개시가 완전하도록 하기 위함이며, 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자에게 발명의 범주를 완전하게 알려주기 위해 제공되는 것이다. 본 발명은 청구항의 기재에 의해 정의될 뿐이다.The features of the present invention and the method for achieving the same will be apparent from the accompanying drawings and the embodiments described below. However, the present invention is not limited to the embodiments described below, but may be embodied in various forms. The present embodiments are provided so that the disclosure of the present invention is complete and that those skilled in the art will fully understand the scope of the present invention. The invention is only defined by the description of the claims.
이하 첨부된 도면을 참조하여 본 발명의 바람직한 실시예에 따른 강재 및 그 제조 방법에 관하여 상세히 설명하면 다음과 같다.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a steel material according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
본 발명에 따른 강재는 중량%로, 탄소(C) : 0.15~0.20%, 실리콘(Si) : 0.3~0.4%, 망간(Mn) : 1.0~1.2%, 구리(Cu) : 0.1~0.2%, 니오븀(Nb) : 0.01~0.02%, 니켈(Ni) : 0.15~0.25%, 크롬(Cr) : 0.15~0.25%, 인(P) : 0.02% 이하, 황(S) : 0.005% 이하, 바나듐(V) : 0.02~0.03% 및 칼슘(Ca) : 0.001~0.003% 를 포함한다.Steel according to the present invention by weight%, carbon (C): 0.15 ~ 0.20%, silicon (Si): 0.3 ~ 0.4%, manganese (Mn): 1.0 ~ 1.2%, copper (Cu): 0.1 ~ 0.2%, Niobium (Nb): 0.01 to 0.02%, Nickel (Ni): 0.15 to 0.25%, Chromium (Cr): 0.15 to 0.25%, Phosphorus (P): 0.02% or less, Sulfur (S): 0.005% or less, Vanadium ( V): 0.02 to 0.03% and calcium (Ca): 0.001 to 0.003%.
상기 성분들 외 나머지는 철(Fe)과 불가피한 불순물로 이루어진다. The remainder of the above components consist of iron (Fe) and unavoidable impurities.
이하, 본 발명에 따른 강재에 포함되는 각 성분의 역할 및 그 함량에 대하여 설명하면 다음과 같다.
Hereinafter, the role and content of each component contained in the steel according to the present invention will be described.
탄소(C)Carbon (C)
탄소(C)는 강도 확보에 기여하는 원소이다.Carbon (C) is an element contributing to securing strength.
상기 탄소는 본 발명에 따른 강재 전체 중량의 0.15~0.20중량%로 첨가되는 것이 바람직하다. 탄소의 첨가량이 0.15중량% 미만일 경우, 강도 향상 효과가 불충분하다. 반대로, 탄소의 첨가량이 0.20중량%를 초과하면, 열영향부에 도상 마르텐사이트(Martensite Austenite constituent, MA)가 생성되어, 열영향부 인성 및 슬라브 표면 품질을 저하시키는 문제점이 있다.
The carbon is preferably added in an amount of 0.15 to 0.20% by weight based on the total weight of the steel according to the present invention. When the amount of carbon added is less than 0.15% by weight, the effect of improving strength is insufficient. On the contrary, when the amount of added carbon exceeds 0.20% by weight, Martensite Austenite constituent (MA) is generated in the heat-affected zone, thereby deteriorating the heat-affected zone toughness and slab surface quality.
실리콘(silicon( SiSi ))
실리콘(Si)은 강 중 탈산제로 작용하며, 고용강화에 따른 강도 확보에 기여한다. Silicon (Si) acts as a deoxidizer in steel and contributes to securing strength due to solid solution strengthening.
상기 실리콘은 본 발명에 따른 강재 전체 중량의 0.3~0.4중량%로 첨가되는 것이 바람직하다. 실리콘의 첨가량이 0.3중량% 미만이면 그 첨가 효과가 불충분하다. 반대로, 실리콘의 첨가량이 0.4중량%를 초과하면, 강재의 인성 및 용접성이 열화되는 문제점이 있다.
The silicon is preferably added in 0.3 ~ 0.4% by weight of the total weight of the steel according to the present invention. If the addition amount of silicon is less than 0.3% by weight, the effect of addition is insufficient. On the contrary, when the addition amount of silicon exceeds 0.4 weight%, there exists a problem that the toughness and weldability of steel materials deteriorate.
망간(manganese( MnMn ))
망간(Mn)은 인성을 열화시키지 않고, 페라이트 생성을 억제하여 Ar3 온도를 낮춤으로써 소입성을 효과적으로 상승시켜 강도 향상에 기여한다.Manganese (Mn) does not deteriorate toughness but suppresses ferrite formation and lowers the Ar3 temperature, thereby effectively increasing the ingot properties and contributing to the strength improvement.
상기 망간은 본 발명에 따른 강재 전체 중량의 1.0~1.2중량%로 첨가되는 것이 바람직하다. 망간의 첨가량이 1.0중량% 미만일 경우, 그 첨가 효과가 불충분하다. 반대로, 망간의 첨가량이 1.2중량%를 초과하면 탄소당량을 높여 용접성을 저해시킨다.
The manganese is preferably added in 1.0 to 1.2% by weight of the total weight of the steel according to the present invention. If the addition amount of manganese is less than 1.0% by weight, the effect of addition thereof is insufficient. On the other hand, if the addition amount of manganese exceeds 1.2 wt%, the carbon equivalent is increased to deteriorate the weldability.
구리(Copper( CuCu ))
구리(Cu)는 고용강화에 기여하여 강도를 향상시키는 역할을 한다. Copper (Cu) contributes to solid solution strengthening and enhances strength.
상기 구리는 본 발명에 따른 강재 전체 중량의 0.1~0.2중량%로 첨가되는 것이 바람직하다. 구리의 첨가량이 0.1중량% 미만일 경우, 그 첨가 효과가 미미하다. 반대로, 구리의 첨가량이 0.2중량%를 초과하는 경우, 강재의 열간가공성을 저하시키고, 용접후 재열균열(Stress Relief Cracking) 감수성을 높이는 문제점이 있다.
The copper is preferably added in 0.1 to 0.2% by weight of the total weight of the steel according to the present invention. When the addition amount of copper is less than 0.1% by weight, the addition effect is insignificant. On the contrary, when the amount of copper exceeds 0.2% by weight, there is a problem of lowering the hot workability of the steel and increasing the susceptibility of stress relief cracking after welding.
니오븀(Niobium ( NbNb ))
니오븀(Nb)은 오스테나이트에 고용되어 오스테나이트의 경화능을 증대시키고, Nb(C, N) 등의 탄질화물을 석출시킴으로써 강도 향상에 기여한다. 또한, 결정립 미세화를 통하여 저온인성 향상에 기여한다. Niobium (Nb) is dissolved in austenite to increase the hardenability of austenite and to precipitate carbonitrides such as Nb (C, N), thereby contributing to strength improvement. In addition, it contributes to improvement of low temperature toughness through grain refinement.
상기 니오븀은 강재 전체 중량의 0.01~0.02중량%로 첨가되는 것이 바람직하다. 니오븀의 첨가량이 0.01중량% 미만일 경우 상기의 니오븀 첨가 효과를 충분히 발휘할 수 없다. 반대로, 니오븀의 첨가량이 0.02중량%를 초과할 경우 강재의 수소유기균열 저항성을 저하시킨다.
The niobium is preferably added in an amount of 0.01 to 0.02% by weight based on the total weight of the steel material. When the addition amount of niobium is less than 0.01% by weight, the effect of adding niobium can not be sufficiently exhibited. On the contrary, when the addition amount of niobium exceeds 0.02 wt%, the hydrogen organic cracking resistance of the steel is lowered.
니켈(nickel( NiNi ))
니켈(Ni)은 저온인성 향상과 강도를 증가시키는데 매우 효과적인 원소이다.Nickel (Ni) is a very effective element to improve low temperature toughness and increase strength.
상기 니켈(Ni)은 본 발명에 따른 강재 전체 중량의 0.15 ~ 0.25 중량%로 첨가되는 것이 바람직하다. 니켈의 첨가량이 0.15 중량% 미만일 경우, 그 첨가 효과가 미미하다. 반대로, 니켈의 첨가량이 0.25 중량%를 초과하는 경우, 강재의 냉간가공성 및 용접성을 저하시킨다. 또한 고가로 인해 제조비용을 크게 상승시킨다.
The nickel (Ni) is preferably added at 0.15 to 0.25% by weight of the total weight of the steel according to the present invention. When the amount of nickel added is less than 0.15% by weight, the effect of addition is insignificant. On the contrary, when the addition amount of nickel exceeds 0.25 weight%, the cold workability and weldability of steel materials will fall. In addition, the high cost greatly increases the manufacturing cost.
크롬(chrome( CrCr ))
크롬(Cr)은 소입성을 증가시켜 강도 향상에 기여한다. 상기 크롬은 본 발명에 따른 강재 전체 중량의 0.15 ~ 0.25 중량%로 첨가되는 것이 바람직하다. 크롬의 함량이 0.15 중량% 미만일 경우, 그 첨가 효과가 미미하다. 반대로, 크롬의 첨가량이 0.25 중량%를 초과하는 경우, 용접 열영향부(HAZ) 인성 열화를 초래하는 문제점이 있다.
Chromium (Cr) increases hardenability and contributes to strength improvement. The chromium is preferably added in an amount of 0.15 to 0.25% by weight based on the total weight of the steel according to the present invention. If the content of chromium is less than 0.15% by weight, the effect of addition is insignificant. Conversely, when the amount of chromium added exceeds 0.25% by weight, there is a problem that the weld heat affected zone (HAZ) toughness deteriorates.
인(P), 황(S)Phosphorus (P), sulfur (S)
인(P)은 강재의 인성, 특히 CTOD(Crack Tip Opening Displacement) 특성을 열화시키는 문제가 있다. 따라서, 본 발명에서는 인의 함량을 본 발명에 따른 강재 전체 중량의 0.02 중량% 이하로 제한하였다.Phosphorus (P) has a problem of deteriorating the toughness of the steel, in particular the crack tip opening displacement (CTOD) characteristics. Therefore, in the present invention, the content of phosphorus is limited to 0.02% by weight or less based on the total weight of the steel material according to the present invention.
황(S)은 재열균열 감수성을 높인다. 따라서, 본 발명에서는 황의 함량을 본 발명에 따른 강재 전체 중량의 0.005 중량% 이하로 제한하였다.
Sulfur (S) increases the reheat crack susceptibility. Therefore, in the present invention, the content of sulfur is limited to 0.005% by weight or less based on the total weight of the steel according to the present invention.
바나듐(V)Vanadium (V)
바나듐(V)은 강력한 소입성 원소로 작용하여 마르텐사이트 상의 형성에 효과적인 원소이다. 또한, 바나듐(V)은 페라이트 상 내에서 탄소와 결합하여 입내 탄화물을 생성시켜 강도를 향상시키고, 고용 탄소를 저감하여 항복비를 감소시키는 역할을 한다.Vanadium (V) is an element effective for forming a martensite phase by acting as a strong incendiary element. In addition, vanadium (V) bonds with carbon in the ferrite phase to produce intragranular carbides to improve the strength and reduce the yield carbon to reduce the yield ratio.
상기 바나듐(V)은 강판 전체 중량의 0.02 ~ 0.03 중량%로 첨가되는 것이 바람직하다. 바나듐(V)의 첨가량이 0.02 중량% 미만일 경우, 그 첨가 효과가 미미하고, 반대로 0.03 중량%를 초과하여 첨가되면 항복비가 증가되는 문제점이 있다.
The vanadium (V) is preferably added in an amount of 0.02 to 0.03% by weight based on the total weight of the steel sheet. When the addition amount of vanadium (V) is less than 0.02 wt%, the effect of addition thereof is insignificant. On the contrary, when vanadium (V) is added in an amount exceeding 0.03 wt%, the yield ratio increases.
칼슘(calcium( CaCa ))
칼슘(Ca)은 황(S)과 친화력이 망간(Mn)보다 우수하여 구상의 CaS 개재물을 형성함으로써 수소유기균열에 악영향을 미치는 MnS 개재물을 감소시킨다.Calcium (Ca) is superior to manganese (Mn) in affinity with sulfur (S), and forms CaS inclusions in spheres, thereby reducing MnS inclusions that adversely affect hydrogen organic cracking.
상기 칼슘은 강재 전체 중량의 0.001~0.003 중량%로 첨가되는 것이 바람직하다. 칼슘의 첨가량이 0.001 중량% 미만일 경우, 그 첨가 효과가 불충분하다. 반대로, 칼슘의 첨가량이 0.003 중량%를 초과하는 경우, 다량의 CaO를 형성하여 강재의 용접성을 저해하는 문제점이 있다.
The calcium is preferably added in an amount of 0.001 to 0.003% by weight based on the total weight of the steel material. When the addition amount of calcium is less than 0.001% by weight, the effect of addition is insufficient. On the other hand, when the addition amount of calcium exceeds 0.003% by weight, a large amount of CaO is formed to deteriorate the weldability of the steel.
본 발명에 따르면 상기 조성 및 후술하는 공정 제어에 의하여, 도 2에 도시된 바와 같이 결정립의 조직을 미세하게 제어하여 폭 방향 및 두께 방향의 재질 편차를 최소화하고, 장시간의 PWHT(Post-Weld Heat Treatment) 이후에도 -50℃ 저온에서 인성이 우수한 강재를 제작할 수 있다.According to the present invention, by controlling the composition and the process control to be described later, as shown in Fig. 2, the texture of the crystal grains is finely controlled to minimize the material deviation in the width direction and the thickness direction, ), It is possible to produce a steel having excellent toughness at a low temperature of -50 ° C.
또한, 본 발명에 따른 강재는 표 2에 나타낸 것과 같이 제조된 직후와 장시간의 PWHT 이후에도 -50℃에서 중심부 평균 충격흡수에너지 30J 이상의 값을 갖는 것을 특징으로 하며, 이를 통해 강재의 저온인성이 우수함을 알 수 있다. 이는 결정립의 미세조직 제어에 따른 결과라 볼 수 있다.Also, the steel according to the present invention is characterized by having a center average impact absorption energy of 30 J or more at -50 ° C. immediately after being manufactured and after a long time PWHT as shown in Table 2, whereby the low temperature toughness of the steel is excellent Able to know. This is a result of microstructure control of crystal grains.
이에 따라, 본 발명에 따른 강재는 우수한 저온인성 특성으로 인해 용접구조용 압력용기나 초대형 컨테이너선의 외판용 소재로 활용될 수 있다.
Accordingly, the steel according to the present invention can be utilized as a pressure vessel for welded structures or as a material for a shell plate of a super large container ship due to its excellent low-temperature toughness characteristics.
이하, 상기 특성을 갖는 본 발명에 따른 강재 제조 방법에 대하여 설명하기로 한다.Hereinafter, a steel manufacturing method according to the present invention having the above characteristics will be described.
도 1은 본 발명의 실시예에 따른 강재 제조 방법을 개략적으로 나타낸 순서도이다.1 is a flow chart schematically showing a steel manufacturing method according to an embodiment of the present invention.
도 1을 참조하면, 도시된 강재 제조 방법은 슬라브 재가열 단계(S110), 열간압연 단계(S120), 냉각 단계(S130) 및 노말라이징(normalizing) 열처리 단계(S140)를 포함한다.
Referring to FIG. 1, the illustrated method for manufacturing a steel product includes a slab reheating step S110, a hot rolling step S120, a cooling step S130, and a normalizing heat treatment step S140.
슬라브 재가열Reheating slabs
슬라브 재가열 단계(S110)에서는 전술한 조성을 갖는 강 슬라브를 재가열하여, 초기 생성되는 오스테나이트의 성장을 최대한 억제하면서 석출물의 재고용 및 균질화 등을 향상시킨다.In the slab reheating step (S110), the steel slab having the above composition is reheated to improve the reuse and homogenization of the precipitate while suppressing the growth of the austenite initially produced.
이때, 슬라브 재가열은 1000~1100℃에서 실시되는 것이 바람직하다. 슬라브 재가열 온도가 1000℃ 미만일 경우, 재가열 후 강 슬라브의 온도가 낮아 압연 부하가 커지는 문제점이 있다. 반면, 가열 온도가 1100℃를 초과하는 경우 결정립 조대화 및 경제성이 문제될 수 있다.At this time, the slab reheating is preferably performed at 1000 to 1100 ° C. When the reheating temperature of the slab is less than 1000 ° C, there is a problem that the temperature of the steel slab is low after reheating, resulting in an increase in the rolling load. On the other hand, when the heating temperature is higher than 1100 ° C, grain coarsening and economical efficiency may become a problem.
또한, 슬라브 재가열은 상기 온도범위에서 1~3시간동안 실시되는 것이 바람직하다. 슬라브 재가열 시간이 1시간 미만인 경우, 석출물의 재고용 효과가 불충분할 수 있다. 반대로, 슬라브 재가열 시간이 3시간을 초과하는 경우, 과도한 가열로 인하여 경제성이 문제될 수 있다.In addition, the slab reheating is preferably performed for 1 to 3 hours in the above temperature range. If the slab reheating time is less than 1 hour, the reclaiming effect of the precipitates may be insufficient. Conversely, if the slab reheating time exceeds 3 hours, economics may be a problem due to excessive heating.
한편, 상기 강 슬라브는 탈류와 게재물 제어를 위해, 황(S) 50ppm 이하가 되도록 LF(Ladle Furnace) 공정을 실시한 이후 RH(Ruhrstahl Heraeus) 2Torr 이하에서 처리시간 10분 이상의 진공 탈가스 공정을 거친 다음 경압하를 통해 제조된 것일 수 있다.
On the other hand, the steel slab is subjected to a LF (Ladle Furnace) process so as to have a sulfur (S) content of 50 ppm or less and then subjected to a vacuum degassing process at a temperature of 2 Torr or less under RH (Ruhrstahl Heraeus) It may be produced by the following softening process.
열간압연Hot rolling
다음으로, 열간압연 단계(S120)에서는 재가열된 강재를 Ar3 이상의 온도에서 열간압연한다.Next, in the hot rolling step (S120), the reheated steel is hot-rolled at a temperature equal to or higher than Ar3.
열간압연은 압연종료온도 850~920℃ 조건으로 실시하는 것이 바람직하다. 압연종료온도가 920℃를 초과하는 경우, 재결정 및 결정립 조대화로 인하여 강도 및 인성 확보가 어렵다. 반면, 압연종료온도가 850℃ 미만일 경우, 이상역 압연에 따른 인성 열화 및 항복비가 높아질 수 있다.The hot rolling is preferably carried out under the conditions of a rolling finish temperature of 850 to 920 占 폚. When the rolling finishing temperature exceeds 920 占 폚, it is difficult to obtain strength and toughness due to recrystallization and crystal grain coarsening. On the other hand, if the rolling finish temperature is less than 850 ° C, the toughness deterioration and yield ratio due to abnormal reverse rolling can be increased.
특히, 열간압연시 패스당 압하력을 증대시켜 이에 따른 중심부의 변형을 최대화하여 압연을 종료한다.
In particular, during hot rolling, the rolling force is increased to maximize the deformation of the center portion, thereby completing the rolling.
냉각Cooling
다음으로, 냉각 단계(S130)에서는 상기 열간압연된 강재를 냉각한다.Next, in the cooling step (S130), the hot-rolled steel material is cooled.
냉각은 5℃/sec 이하의 평균냉각속도로 실시되는 것이 바람직하고, 보다 바람직하게는 공냉 방식으로 실시하는 것을 제시할 수 있다. 냉각시 평균냉각속도가 5℃/sec를 초과하는 경우, 제조되는 강의 강도는 높일 수 있으나, 냉각시 강 내부에 존재하는 수소 등의 성분이 충분히 확산되기 어려워지므로, 수소유기균열 특성이 저하될 수 있다. 또한, 냉각은 상온까지 이루어질 수 있다.
The cooling is preferably carried out at an average cooling rate of 5 DEG C / sec or less, and more preferably, it can be carried out by air cooling. If the average cooling rate during cooling exceeds 5 DEG C / sec, the strength of the produced steel can be increased, but the components such as hydrogen present in the steel during cooling can not be sufficiently diffused, have. Further, the cooling can be performed up to room temperature.
노말라이징Normalizing 열처리 Heat treatment
다음으로, 노말라이징 열처리 단계(S140)에서는 냉각된 강재를 열처리 로(furnace)에 장입하여 890~920℃에서 노말라이징 열처리하여 제조되는 강재의 조직을 미세화 및 균질화하며, 저온인성을 향상시킨다.Next, in the normalizing heat treatment step (S140), the cooled steel material is charged into a furnace, and the steel material produced by the normalizing heat treatment at 890 to 920 ° C is refined and homogenized to improve the low temperature toughness.
이때, 노말라이징 열처리 온도는 Ac3점 이상이어야 하는데, 이는 재결정에 의해 오스테나이트 결정립이 미세화되어 강도, 인성이 동시에 향상되기 때문이다.At this time, the normalizing heat treatment temperature should be equal to or higher than Ac3 point, because the austenite grains are refined by recrystallization, and strength and toughness are simultaneously improved.
한편, 본 발명의 발명자들은 오랜 연구를 거듭한 결과, 강재의 두께에 따라 노말라이징 열처리 시간이 하기 [식 1]을 따를 때 저온인성이 보다 향상되는 것을 알아내었다. On the other hand, the inventors of the present invention have found out that the low temperature toughness is improved when the normalizing heat treatment time according to the following formula [1] is further improved according to the thickness of the steel.
[식 1] [Formula 1]
t = A × T + 10t = A x T + 10
(여기서, t : 열처리 시간(min), T : 강재 두께(mm), 40<T≤60인 경우 A=1.5, 60<T≤80인 경우 A=1.6, 80<T인 경우, A=1.7로 정의함)A = 1.5 when 60 <T≤80, A = 1.6 when 80 <T≤80, A = 1.7 when 80 <T, )
일례로, 두께가 80mm인 강재를 제조하는 경우, 노말라이징 열처리 시간은 138분이다.For example, when a steel material having a thickness of 80 mm is manufactured, the normalizing heat treatment time is 138 minutes.
한편, 도면으로 도시하지는 않았으나, 노말라이징 열처리 단계(S140) 후에는 공냉 등의 방식으로 강재를 상온까지 냉각할 수 있다.
On the other hand, although not shown in the drawing, after the normalizing heat treatment step (S140), the steel material can be cooled to room temperature by a method such as air cooling.
실시예Example
이하, 본 발명의 바람직한 실시예를 통해 본 발명의 구성 및 작용을 더욱 상세히 설명하기로 한다. 다만, 이는 본 발명의 바람직한 예시로 제시된 것이며 어떠한 의미로도 이에 의해 본 발명이 제한되는 것으로 해석될 수는 없다. Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.
여기에 기재되지 않은 내용은 이 기술 분야에서 숙련된 자이면 충분히 기술적으로 유추할 수 있는 것이므로 그 설명을 생략하기로 한다.
Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.
1. 강재의 제조1. Manufacture of Steel
표 1에 나타낸 조성을 갖는 실시예 1~2 및 비교예 1~2의 300mm 두께 강 슬라브를 마련하였다.300 mm thick steel slabs of Examples 1 to 2 and Comparative Examples 1 and 2 having the compositions shown in Table 1 were prepared.
[표 1][Table 1]
이후, 강 슬라브를 1100℃로 2시간 동안 재가열한 후, 압연종료온도 920℃ 조건으로 열간압연을 실시한 후, 공냉 방식으로 25℃까지 냉각하였다. 이후, 강재를 905℃까지 가열하여 하기 [식 1]에 따른 열처리 시간, 즉 180분 동안 노말라이징(normalizing) 열처리를 실시한 후, 공냉 방식으로 25℃까지 냉각하여, 100mm 두께의 강재를 제조하였다.Thereafter, the steel slab was reheated at 1100 占 폚 for 2 hours, then subjected to hot rolling at a rolling finish temperature of 920 占 폚 and then cooled to 25 占 폚 by air cooling. Thereafter, the steel material was heated up to 905 占 폚, subjected to a normalizing heat treatment for 180 minutes, and then cooled to 25 占 폚 in an air cooling manner to prepare a steel material having a thickness of 100 mm.
[식 1], 즉 t = A × T + 10 [Equation 1], i.e., t = A x T + 10
(여기서, t : 열처리 시간(min), T : 강재 두께(mm), 40<T≤60인 경우 A=1.5, 60<T≤80인 경우 A=1.6, 80<T인 경우, A=1.7로 정의함)A = 1.5 when 60 <T≤80, A = 1.6 when 80 <T≤80, A = 1.7 when 80 <T, )
상기 [식 1]에서, 강재 두께(T)=100mm, A=1.7을 적용하였으며, 이에 따라 열처리 시간(t)은 180분이었다.In the above formula 1, the steel material thickness (T) = 100 mm and A = 1.7 were applied, and the heat treatment time (t) was 180 minutes.
그런 다음, 시편에 대해 610℃에서 각각 3시간, 12시간 동안 PWHT를 수행하였으며, 이때 400℃ 이상에서는 평균 승온/냉각속도를 70℃/hr로 하였다.
PWHT was then applied to the specimens at 610 ° C for 3 hours and 12 hours, respectively, at an average temperature rise / cooling rate of 70 ° C / hr above 400 ° C.
2. 물성 평가2. Property evaluation
표 2는 실시예 1~2 및 비교예 1~2에 따라 제조된 직후와 각각 3시간, 12시간의 PWHT가 추가 실시된 강재에 대해 -50℃에서의 충격 에너지 값을 나타낸 것이다.Table 2 shows the impact energy values at -50 ° C for steel materials immediately after PWHT prepared according to Examples 1 and 2 and Comparative Examples 1 and 2 and for PWHT added for 3 hours and 12 hours, respectively.
이때, 충격 에너지는 샤르피 3회 중심부 평균 충격 흡수에너지를 의미하며, ASTM E23에 의거한 샤르피 충격시험을 통하여 측정하였다.In this case, the impact energy means the center average impact absorption energy of Charpy three times, and was measured by Charpy impact test according to ASTM E23.
[표 2][Table 2]
표 2를 참조하면, 본 발명에 따른 조성을 만족하는 실시예 1~2에 따라 제조된 두께 100mm 강재의 경우, 제조된 직후와 각각 3시간, 12시간의 PWHT가 추가 실시된 상태 모두 -50℃에서 중심부 평균 충격흡수에너지가 35J 이상의 값을 나타내어 저온인성이 우수함을 알 수 있다.Referring to Table 2, in the case of the 100 mm-thick steel material prepared according to Examples 1 and 2 satisfying the composition according to the present invention, it was found that the steel material was produced at a temperature of -50 ° C The average impact absorption energy of the central portion is 35 J or more, which is excellent in low temperature toughness.
이에 반해, 본 발명에 따른 조성을 만족하지 않는 비교예 1~2에 따라 제조된 두께 100mm 강재의 경우, 제조된 직후와 각각 3시간, 12시간의 PWHT가 추가 실시된 상태 모두 -50℃에서 중심부 평균 충격흡수에너지가 대략 16~25J 수준으로 목표하는 30J에 미치지 못 하여 저온인성에 취약함을 알 수 있다.
On the contrary, in the case of the 100 mm-thick steels prepared according to Comparative Examples 1 and 2 which did not satisfy the composition according to the present invention, the PWHT was added at a temperature of -50 ° C. for 3 hours and 12 hours, The impact absorption energy is about 16 ~ 25J, which is not enough to reach the target 30J, so it is vulnerable to low temperature toughness.
도 2는 본 발명의 실시예 1에 따라 제조된 강재의 광학현미경(Optical Microscope: OM) 사진이다.2 is an optical microscope (OM) photograph of a steel material produced according to Example 1 of the present invention.
도 2를 참조하면, 실시예 1에 따라 제조된 두께 100mm 강재의 경우, 결정립이 미세하고, 균일화된 조직을 가짐을 확인할 수 있다. 이는 폭 방향 및 두께 방향의 재질편차 특성 향상뿐만 아니라 장시간의 PWHT 이후에도 -50℃ 저온에서의 인성 향상에 기여한다.
Referring to FIG. 2, it can be confirmed that the 100 mm-thick steel material produced according to Example 1 had fine grains and a uniform texture. This not only improves the material deviation characteristics in the width direction and the thickness direction, but also contributes to improvement in toughness at -50 캜 and low temperature even after long-time PWHT.
이상에서는 본 발명의 실시예를 중심으로 설명하였지만, 당업자의 수준에서 다양한 변경이나 변형을 가할 수 있다. 이러한 변경과 변형이 본 발명의 범위를 벗어나지 않는 한 본 발명에 속한다고 할 수 있다. 따라서 본 발명의 권리범위는 이하에 기재되는 청구범위에 의해 판단되어야 할 것이다.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.
S110 : 슬라브 재가열 단계
S120 : 열간압연 단계
S130 : 냉각 단계
S140 : 노말라이징 열처리 단계S110: Slab reheating step
S120: Hot rolling step
S130: cooling step
S140: Normalizing heat treatment step
Claims (5)
상기 재가열된 강재를 Ar3 이상의 온도에서 열간압연하는 단계;
상기 열간압연된 강재를 냉각하는 단계; 및
상기 냉각된 강재를 890~920℃에서 노말라이징(normalizing) 열처리하는 단계;를 포함하는 것을 특징으로 하는 강재 제조 방법.By weight%, carbon (C): 0.15-0.20%, silicon (Si): 0.3-0.4%, manganese (Mn): 1.0-1.2%, copper (Cu): 0.1-0.2%, niobium (Nb): 0.01 ~ 0.02%, Nickel (Ni): 0.15 ~ 0.25%, Chromium (Cr): 0.15 ~ 0.25%, Phosphorus (P): 0.02% or less, Sulfur (S): 0.005% or less, Vanadium (V): 0.02 ~ 0.03 %, Calcium (Ca): reheating the steel slab consisting of 0.001 ~ 0.003% and the remaining iron (Fe) and inevitable impurities at 1000 ~ 1100 ℃;
Hot-rolling the reheated steel at a temperature equal to or greater than Ar3;
Cooling the hot rolled steel material; And
And performing a normalizing heat treatment on the cooled steel material at 890 to 920 캜.
상기 열간압연은
압연종료온도 850~920℃ 조건으로 수행되는 것을 특징으로 하는 강재 제조 방법.The method of claim 1,
The hot rolling
And a rolling finish temperature of 850 to 920 占 폚.
상기 노말라이징 열처리는
하기 식 1에 의해 정해지는 시간 동안 실시되는 것을 특징으로 하는 강재 제조 방법.
[식 1]
t = A × T + 10
(여기서, t : 열처리 시간(min), T : 강재 두께(mm), 40<T≤60인 경우 A=1.5, 60<T≤80인 경우 A=1.6, 80<T인 경우, A=1.7로 정의함)The method of claim 1,
The normalizing heat treatment
Steel manufacturing method characterized in that carried out for a time determined by the following formula (1).
[Formula 1]
t = A x T + 10
A = 1.5 when 60 <T≤80, A = 1.6 when 80 <T≤80, A = 1.7 when 80 <T, )
상기 냉각은
공냉 방식으로 실시되는 것을 특징으로 하는 강재 제조 방법. The method of claim 1,
The cooling
Wherein the cooling water is cooled in an air cooling manner.
12시간 PWHT(Post-Weld Heat Treatment) 이후, -50℃에서 두께방향 중심부 평균 충격흡수에너지 30J 이상을 나타내는 것을 특징으로 하는 강재.By weight%, carbon (C): 0.15-0.20%, silicon (Si): 0.3-0.4%, manganese (Mn): 1.0-1.2%, copper (Cu): 0.1-0.2%, niobium (Nb): 0.01 ~ 0.02%, Nickel (Ni): 0.15-0.25%, Chromium (Cr): 0.15-0.25%, Phosphorus (P): 0.02% or less, Sulfur (S): 0.005% or less, Vanadium (V): 0.02-0.03 %, Calcium (Ca): 0.001 ~ 0.003% and the remaining iron (Fe) and inevitable impurities,
, And exhibits an average impact absorption energy of 30 J or more in the thickness direction center at -50 캜 after 12 hours of post-weld heat treatment (PWHT).
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| WO2017105109A1 (en) * | 2015-12-15 | 2017-06-22 | 주식회사 포스코 | High-strength steel material having excellent low-temperature strain aging impact properties and method for manufacturing same |
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| KR101253890B1 (en) * | 2010-12-28 | 2013-04-16 | 주식회사 포스코 | Ultra thick steel sheet for pressure vessel having excellent central properties and hydrogen induced cracking resistance, and method for manufacturing the same |
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| WO2017105109A1 (en) * | 2015-12-15 | 2017-06-22 | 주식회사 포스코 | High-strength steel material having excellent low-temperature strain aging impact properties and method for manufacturing same |
| CN108368594A (en) * | 2015-12-15 | 2018-08-03 | 株式会社Posco | High strength steel and its manufacturing method with excellent low temperature strain-aging impact characteristics and welding heat affected zone impact characteristics |
| CN108368594B (en) * | 2015-12-15 | 2020-12-25 | 株式会社Posco | High-strength steel material having excellent low-temperature strain aging impact characteristics and weld heat-affected zone impact characteristics, and method for producing same |
| US11136653B2 (en) | 2015-12-15 | 2021-10-05 | Posco | High-strength steel material having excellent low-temperature strain aging impact properties and welding heat-affected zone impact properties and method for manufacturing same |
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